You would have come across many people saying "Bless You" while someone sneeze.
Have you ever wonder why they say it or did you ask them why?
Sources say they originated thousands of years ago.
"God Bless You" is attributed to Pope Gregory the Great, who uttered it in the 6th century during a plague epidemic.
Sneezing is an obvious symptom of one form of the plague during that time.
Some say that the heart stops momentarily when someone sneeze and his or her back to life is welcomed by saying "Bless You".
But health related articles say that heart wont stop during sneeze and it is a misconception.
Some believe that evil spirits use the sneeze as an opportunity to enter a person's body.
Saying "bless you" would stop this window of opportunity.
In general sneezing is a sign of cold or allergy and can be provoked in the sunlight or from smelling a strong odor.
Whatever may be the reason, we persist in the custom of saying "Bless You" out of common courtesy or habit.